1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor substrate having an SOI (silicon on insulator) structure. The present invention also relates to a method for manufacturing a semiconductor device using the semiconductor substrate. Note that a semiconductor device in this specification refers to any device which can function by utilizing semiconductor characteristics.
2. Description of the Related Art
In recent years, VLSI technology has been dramatically progressed, and an SOI structure by which speeding up and low power consumption are realized has attracted attention. This technology allows an active region (channel formation region) of a field-effect transistor (FET), which has been formed of bulk single crystal silicon, to be formed of a single crystal silicon thin film. It is known that a MOS field-effect transistor manufactured using an SOI structure has lower parasitic capacitance than that manufactured using a conventional bulk single crystal silicon substrate, which is an advantage in increasing speed.
Examples of SOI substrates include SIMOX substrates and bonded substrates. For example, an SOI structure of a SIMOX substrate is obtained as follows: oxygen ions are implanted into a single crystal silicon substrate and heat treatment is performed at 1300° C. or more to form a buried oxide (BOX) layer, so that a single crystal silicon thin film is formed on the surface. For a SIMOX substrate, oxygen ion implantation can be controlled precisely and thus a single crystal silicon thin film having an even thickness can be formed with high precision; however, there is a problem with costs because a long period of time is required for oxygen ion implantation. In addition, there is another problem in that a single crystal silicon thin film is likely to be damaged during oxygen ion implantation.
An SOI structure of a bonded substrate is obtained as follows: two single crystal silicon substrates (a base substrate and a bond substrate) are bonded to each other with an oxide film interposed therebetween and one of the two single crystal silicon substrates (the bond substrate) is thinned from the rear surface thereof (a surface opposite to the bonded surface), so that a single crystal silicon thin film is formed. As a thinning method, a technique utilizing hydrogen ion implantation, which is called Smart Cut (registered trademark), has been suggested because it is difficult to form an even and thin single crystal silicon thin film by grinding and polishing (for example, see Reference 1: Japanese Published Patent Application No. H5-211128).